Chapter SixEnhanced Mode Firmware DescriptionIntroductionThe Enhanced mode is an interface architecture which allows the AHA-1740A/1742A/1744 to take full advantage of the EISA bus facilities. It utilizes a dis-tinct hardware interface control logic, known as the configuration chip. This permitsfeatures such as full 32-bit addressing and the entire EISA register set to be used.This mode is not compatible with versions of the ASW-1400 series of software manag-ers before version 3.0. In order to use the Enhanced Mode, the AHA-1740A/1742A/1744 must be correctly reconfigured by using the configuration utilitydescribed in Chapter Three, Installation. The AHA-1740A/1742A/1744 is not capableof simultaneous operation in Standard and Enhanced Modes.Operations using the Enhanced Mode utilize a mailbox interface which is substan-tially different from the Standard Mode. The principal difference is the use of a sin-gle mailbox structure which is serviced at a rate that prevents overwriting. Themailbox structure is described in detail in the section on EISA Expansion Identifiersin Chapter Four, Hardware Functional Description. The components of the mailboxare:zCD0 Mailbox Out PointerzCD1 Mailbox Out PointerzCD2 Mailbox Out PointerzCD3 Mailbox Out PointerzCD4 Attention RegisterzCD5 Enhanced Mode Control RegisterzCD6 Interrupt Status RegisterzCD7 Enhanced Mode Status RegisterzCD8 Mailbox In PointerzCD9 Mailbox In PointerzCDA Mailbox In PointerzCDB Mailbox In PointerOperations using the mailbox begins with the host assembling an Enhanced ControlBlock (ECB) in memory. The host then stores the pointer to the ECB in the MailboxOut, provided that bit 2 of the SCD7 Status register (MBO empty) is true. Due to thespeed with which the AHA-1740A/1742A/1744 services the mailbox, the MBO will al-most always be empty.6-1
